An experimental study on shortening of ddt distance for pulse detonation engines

Paper number

IAC-06-C4.5.09

Author

Mr. Ryuji Nakawatase, Kyushu University, Japan

Coauthor

Mr. Hiroaki Miyazawa, Kyushu University, Japan

Coauthor

Prof. Shigeru Aso, Kyushu University, Japan

Coauthor

Dr. Yasuhiro Tani, Kyushu University, Japan

Year

2006

Abstract

Pulse Detonation Engines (PDEs) have the potential to revolutionize aerospace propulsion system for future aerospace vehicles. One reason for this seems to be the promise of high efficiency due to the fact that PDE cycles operate with near-constant volume combustion. Furthermore, it is often argued that PDEs have fewer parts and are much less mechanically complex than other thrust producing systems. In turn, this makes them considerably less expensive. To realize PDE, a detonation should be occurred in a short distance. The internal obstacles, for example Shchelkin spirals and orifice plates are used to shorten the Deflagration-to-Detonation Transition (DDT) distance. These obstacles enhancing DDT cause reductions of thrust and make purge hard. Therefore, in this study, to enhance DDT, a new device which hardly blocks the flow path and hardly causes associated losses in propulsive efficiency had been designed and evaluated to use for PDEs. The design concept of a new device has been to raise the reflection frequency of the compression waves caused by combustion, to make “an explosion in an explosion” easy to cause. Therefore, a tube having smaller diameter has been installed in a detonation tube. The losses this tube was almost skin friction drag only.

The dimensions of the detonation tube tested were 50.0 mm diameter by 2.0 m long. The DDT enhancing device was an open tube measures 16.1 mm diameter by 1.0 m long by 2.8 mm thick. The device was installed in the center of the detonation tube and its head was located at 100 mm from the closed end of the tube. A two-needle spark igniter which was located at the closed end was used to ignite the mixtures. To detect combustion waves, two-needle ion probes were mounted along the tube wall with 200 mm intervals. Experiments were performed with hydrogen and oxygen mixtures initially at 0.1013 MPa. The equivalence ratios were 0.3, 0.4, 1.8 and 2.0.

At an equivalence ratio of 0.3, in the case with the DDT enhancing device, the DDT distance was 0.5 m while in the case without the device, the distance was 1.7 m. As for other equivalence ratios, the DDT distance was similarly shortened.

The new DDT enhancing device was developed. The experimental results showed that the device was very useful for shortening the DDT distance. Therefore, applying this device to PDEs makes possible shorter detonation tubes and higher frequency cycle operations.

Abstract document

IAC-06-C4.5.09.pdf

Manuscript document

IAC-06-C4.5.09.pdf (🔒 authorized access only).

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